582 BACTERIOLOGY. 



quently afforded to the tissues by an attack of infection 

 or following upon vaccination against infection, was 

 due rather to an abstraction from the tissues, by the 

 organisms that were concerned in the primary attack, 

 of a something that is necessary to the growth of the 

 infecting organism should it gain entrance to the body 

 at any subsequent time. This view is known as the 

 " exhaustion hypothesis" 



As to the exhaustion hypothesis of Pasteur, there is, 

 as yet, no evidence whatever for its support ; and, in 

 fact, in the light shed by more recent investigations this 

 is probably the least tenable of any of the several hy- 

 potheses advanced in explanation of immunity. The 

 work of Bitter, 1 which was undertaken with the view 

 of determining if, in the process of acquiring immunity, 

 there occurred this exhaustion from the tissues of mate- 

 rial necessary to the growth of bacteria that might gain 

 entrance to them at some later date, gave only negative 

 results. The flesh of animals in which immunity had 

 been produced contained all the elements necessary for 

 the growth and nutrition of the bacteria against which 

 the animals had been protected, just as did the flesh of 

 non-vaccinated animals. 



THE PHAGOCYTOSIS THEORY OF METCHNIKOFF. 

 In 1884 Metchnikoff 2 published the first of a series 

 of observations upon the behavior of certain of the 

 mesodermal cells of lower animals toward insoluble 

 particles that may be present in the tissues of these 

 animals. The outcome of these investigations was the 

 establishment of his well-known doctrine of phago- 

 cytosis, the principle of which is that the wandering 



1 Zeitschrift fur Hygiene, 1888, Bd. iv. 



2 Arbeiten aus dem Zoologischen Institut der TJniversitat Wien, 

 1884, Bd. v. Fortschritte der Medicin, 1884, Bd. ii. 



